As is known to those versed skilled in the art, cooling systems conventionally comprise a compressor, a condenser through an expansion device and an evaporator. These components are fluidly connected to each other so as to define a circuit for the circulation of a refrigerant fluid which is able to change state and temperature throughout the cooling system. All functional dynamics of a conventional cooling system is widely known by technicians skilled in the art, and is widely disclosed in the specialized technical literature.
It is also known to the skilled technicians in the art that certain conventional cooling systems, like those used in domestic refrigerators comprise a traditional arrangement wherein the expansion device it is a capillary tube, physically arranged in contact (welded or rolled up) to the outlet pipe of the evaporator, acting as a heat exchanger.
The general principle of this arrangement is to optimize the efficiency of the cooling system through forced cooling of the refrigerant flowing in the expansion device, which provides a reduced restriction to flow, an increase of the specific refrigerating effect and the resulting increased the system cooling capacity.
As is known to those versed skilled in the art, this traditional arrangement shown functional by the fact that the temperature of the refrigerant leaving the evaporator is lower than the temperature of the refrigerant leaving the condenser and is directed to the device expansion. Thus, the physical contact between the capillary and the evaporator outlet pipe (internal heat exchanger) creates conditions to cool the refrigerant flowing into the capillary tube.
On the other hand, they are also known multiple evaporative cooling systems, or integrated cooling systems at least one compressor, at least one condenser, at least two devices of expansion and at least two evaporators which operate so independently at different temperature ranges and pressure. The functional dynamics of this type of cooling system is extremely functional dynamics similar to conventional cooling systems.
In general, the constructive options and the application possibilities of multiple evaporative cooling systems are vast and already well explored in patent documents.
From the constructive viewpoint, PCT/BR2011/000120 describes, for example, a double evaporation cooling system specially built for a reciprocating compressor with double suction provided with two suction inlets on a single compression chamber, or an integrated dual evaporator cooling system in a conventional reciprocating compressor further comprising an additional way, a single fluid selector device, in particular a selector arranged fluids coming from the two evaporation lines. Both compressors provided in PCT/BR2011/000120 enable the construction of a multiple evaporative cooling system.
A typical instantiation of a multi-evaporation cooling system is illustrated in FIG. 1.
Such a system is fundamentally comprised of a double suction reciprocating compressor COMP, by a condenser COND and a feeder AL which extend two evaporation lines.
The first evaporation line is composed of a capillary tube (PDE which defines a first internal heat exchanger PTCI) and a first evaporator PEVAP. Similarly, the second evaporation line is composed of capillary tube SDE (that defines a second internal heat exchanger STCI) and a second evaporator SEVAP.
Of course, the operating principle of each line and evaporation is analogous to the functional principle of a conventional cooling system formed by a traditional arrangement as described above.
It happens, however, that when this traditional arrangement is emulated on a multi-evaporation cooling system, serious problems may occur and, more particularly, serious problems may occur when observing a large increase in thermal load on only one of the evaporators.
This is because, as is known to those versed skilled in the art, the restriction to flow of a capillary tube tends to vary depending on its dimensional characteristics (usually fixed) and depending on the temperature (usually variable) at which said capillary tube is exposed, whether the temperature of the refrigerant that circulate around there, or by an external heat source. In general, the hotter the temperature of exposure, the greater the restriction of the capillary tube.
Thus, returning to refer to FIG. 1, if, for example, the first evaporator PEVAP suffers a great increase of the thermal load (when applied to a refrigerator, when it receives hot or equivalent food), it is normal to occur rise in temperature of the refrigerant exiting the evaporator.
Whereas the first internal heat exchanger PTCI is substantially linked to the temperature of the refrigerant exiting the evaporator, it is expected the heating of the refrigerant flowing in the first expansion device PDE. Consequently, it is expected the increased restriction to flow in said first PDE expansion device.
The increasing restriction to the flow of said first expansion device PDE, due to the increase in its exposure temperature, generates two major interrelated problems, which: (I) The gradual reduction of the supply fluid coolant first evaporator PEVAP triggered by gradually increasing restriction to flow of the first PDE expansion device; and (II) the gradual superloading of refrigerant from the second evaporator SEVAP triggered by cooling the second expansion device SDE caused by excess refrigerant that does not reach the first evaporator.
These conditions are illustrated schematically in FIG. 2, which illustrates comparative graphs of the temperature of the internal heat exchangers and STCI PTCI, and restricting the expansion devices (capillaries) PDE and EDS. As you can see, from the introduction of heat load (time A) in the first compartment evaporator PEVAP the overheating increases, forcing the temperature increase of the first internal heat exchanger PTCI. Consequently, the restriction of the first PDE expansion device increases, forcing the coolant transfer to the second evaporator SEVAP. The second evaporator SEVAP tends to be superloaded characteristic in which the liquid front moves beyond the outlet of the evaporator flooding the second internal heat exchanger STCI and forcing reducing its temperature. Consequently, the restriction of the second expansion device SDE decreases, increasing the transfer of refrigerant to the second evaporator SEVAP and consequently increasing overheating the first evaporator PEVAP due to lack of coolant.
In other words: If one of the evaporators “warm” due to its increased thermal load, it is likely that this same evaporator stop being fed and in return, it is likely that the other evaporator is superloaded. All this occurs due to the redistribution of refrigerant that occurs between the evaporation lines due to the interaction between the outlet temperature of the evaporator and the internal heat exchanger.
Due to the variation restriction of the expansion device, the cooling capacity of both evaporators are compromised affecting the temperature of the compartments. In the case of the system illustrated in FIG. 1, the temperature of the first evaporator PEVAP increases because the large restriction to the first PDE expansion device imposes an evaporator drying forcing the fall of heat exchange effectiveness, drastically reducing its capacity. In turn, the reduction of the second expansion device SDE restriction requires an increase in the evaporating temperature and, in turn, increase the compartment temperature.
The present prior art does not include any technical solution aimed to solve the problem, and is based on this scenario that arises the invention in question.